The present invention relates in general to flexible face signs, and in particular to a new and useful flexible face sign having a uniformly illuminated display surface.
Flexible face signs have been used for many years in outside environments where large illuminated back-lit displays are necessary such as in gas stations, strip malls, convenience stores and the like. Two major problems in constructing and utilizing signs of this design are firstly, how to maintain the flexible face in a taut semi-rigid condition for a relatively long service life while at the same time permitting the sign face to be replaced, and secondly, how to illuminate the flexible face from the rear so that the uniform luminosity is achieved.
Various structures are known for solving the first problem. Among them is U.S. Pat. No. 5,255,466 assigned to the owner of the present application, which discloses a unique anchoring system for the edges of the flexible face.
Various attempts also exist in the prior art for solving the second problem. This involves two basic approaches. The first is using internal reflectors to distribute the light from the light source and the second is by placing an element in front of the light source to spread the luminosity. Both approaches seek to reduce "hot spots" which appear as areas of high luminosity in the immediate vicinity of the light source and which further has the geometry of the light source. For example, due to the elongated nature of most flexible face signs, it has been known to utilize florescent tubes in various arrays within the sign enclosure. This produces elongated hot spots in front of each florescent tube. Point sources of light have also been utilized but these produce circular hot spots if no special measures are taken to distribute the light.
U.S. Pat. No. 1,737,238 uses curved side reflectors which operate in conjunction with v-shaped reflectors to direct light forwardly to the back of an illuminated panel.
The use of a curved reflector behind a fluorescent tube is disclosed in U.S. Pat. No. 3,546,438. The light is directed into the edge of a light guide and thus used for a different purpose then the even illumination of a broad sign surface.
An even more complex mechanism for evenly distributing light on a back lit display which also includes a screen or light diffuser immediately in front of the light, is disclosed in U.S. Pat. No. 3,957,351. A screen is used in front of a light source which has a back reflector for directing the light forwardly.
The use of a multi-layered interference mirror for spreading out light in a lighting device is shown in U.S. Pat. No. 4,161,015.
The use of fluorescent pigment across a back lit display sign is disclosed in U.S. Pat. No. 4,424,449, as an alternate technique for evening out the illumination of a large illuminated sign.
An earlier use for a light reflecting film used to even out light distribution is found in U.S. Pat. No. 4,729,068. This patent shows the use of reflecting areas having a specific density distribution for varying the amount of light going through the otherwise transparent substrate.
A patent which is relevant to the use of side mirrors at an angle to direct light forwardly is U.S. Pat. No. 4,933,814.
U.S. Pat. Nos. 4,787,708 and 4,883,641, use a prismatic reflecting arrangement for distributing light across a surface. U.S. Pat. Nos. 4,912,605 and 5,186,530 use light guides for conveying light from a point source along a light guide and thereafter laterally out of the light guide to illuminate a light surface.
U.S. Pat. No. 4,937,716 discloses a light escapement port with varying transmissivity for producing a constant illumination across the port. A longitudinal specular light reflector which is partly transmissive and made of one or more dielectric interfaces is also used.
A need remains for a well-engineered and robust construction which produces even luminosity across the broad flexible face of a flexible face sign, and which in addition, facilitates replacement of light sources in the sign and is capable of weathering an outdoor environment for long periods of time with minimum maintenance.